Validity. The present study showed the ski ergometer to be valid for evaluating V˙O2 at submaximal and maximal exercise stages in the upper body of cross-country skiers. After the preliminary test, three tests were performed because of a possible learning effect following on test 1, caused by unfamiliarity with the apparatus and possible discomfort wearing the test equipment during poling. This was not necessary when measuring V˙O2peak since there were no significant differences between V˙O2peak on the preliminary test and any of the other tests. A methodological problem was introduced by using Jaeger EOS-sprint to measure V˙O2 on the ski ergometer and Cosmed K2 in the field-test, since Cosmed K2 sets R to 1 and overestimates V˙O2peak if R is in reality higher. Cosmed K2 has been found, by others, to be a reliable and valid apparatus for measurement of oxygen uptake (6,13). To correct V˙O2 measured with the Cosmed K2, equation 1 was used with R-values from test 3 on the ski ergometer. However, we still do not know whether these values were representative for the real R in the field-test, but it is reasonable to believe that the R-values were close to 1.10 as on the ski ergometer. V˙O2peak measured on the ski ergometer (N = 6) was 4.08 L·min−1 (0.24) and was not significantly different from V˙O2peak in the field-test (N = 6) which was 3.91 L·min−1(0.35). The ski ergometer is considered to be very spesific for cross-country skiing as indicated by the perception of the skier subjects.
Reliability. The present study showed the ski ergometer to be reliable for evaluating V˙O2 in the upper body of cross-country skiers. Test-retest correlation for V˙O2 was high (r = 0.98, P < 0.001). The most obvious test for evaluating the ski ergometer was to perform a double poling test in the field, while the subjects were cross-country skiing. The correlation between the two tests was high (r = 0.93,P < 0.001). This alternative-form reliability provides a useful measure for evaluating tests (1).
From a metabolical point of view V˙O2 was expected to be the same at corresponding exercise stages in different tests, regardless of whether the exercise stages were given in an increasing or decreasing manner. The reason for choosing 4 min at each exercise stage was that it normally takes 2-3 min to reach a steady rate V˙O2 after changing the power output (2). The risk of starting at 70% of V˙O2peak was that it could be over the anaerobic threshold in the upper body of the test subjects. If this were to be the case, differences in V˙O2 between increasing and decreasing exercise stages could be expected. V˙O2 at a lower exercise stage could then be higher because an oxygen deficit had been developed, causing a higher cost of poling (2). For all subjects in the present study one had reason to believe that 70% of V˙O2peak was lower than anaerobic threshold in upper body compared with corresponding values in running (7). A continuous protocol was used because others (28) did not find differences in V˙O2peak between using discontinuous or continuous protocols. A pilot study had shown that an increase of 20 W on the ski ergometer gave a change in V˙O2 of approximately 5 mL·kg−1·min−1, which also corresponded with the increase of 15 W as obtained by Mygind et al. (18) in a continuous protocol for measuring V˙O2peak. A plateau for V˙O2 was observed for all subjects, while testing V˙O2peak, despite of further increase in the rate of exercise during work on the ski ergometer and in the field-test, and is therefore a natural criterion for reaching V˙O2peak. When measuring V˙O2peak in the field, care was taken to choose moderately steep hills so that use of maximal force would not be necessary. Use of maximal force would squeeze muscle capillaries, which, in turn, would obstruct local blood flow and limit peripheral oxygen transport (15,24).
If observed power output varied much for the same exercise stages in different tests, the ergometer would not have been of much use. Correlation between power output at the same exercise stages in tests 2 and 3 was high (r = 0.995). Theoretically, the same power output were expected from one test to another when the same values were used in equation 1. Small differences in observed watt between tests were observed and may have been caused by friction between the wheels of the platform and the rail, which may differ somewhat depending on the exact location of the subject on the platform. By standing at the front or back of the platform, the friction may increase a little because of more intense pressure on the wheels and increase the power output somewhat. The drawback of increased friction, when the platform is rolling forward, during the double poling is compensated for by slower rolling of the platform backward during preparation for the next poling. The same is true when the subject stands in the middle of the platform. To avoid variation between tests, the exact location of subjects on the platform could have been controlled by instructing subjects where to position themselves. This was not done because one wanted the subjects to move their legs as naturally as when skiing. The tightness of the elastic wires connected to the poles may have changed during the test period and lead to changes in observed power output between tests. In the same manner, the friction between the pole wheels and the rail could change, depending on how well the rail was greased, and lead to small changes in observed power output. The 2.0% coefficient of variation must be considered as small and did not lead to significant changes in V˙O2 at any exercise in the present study.
No significant differences for V˙O2 at the same exercise stages between any test was as expected, since there were no significant differences between observed power output(W) at the same exercise stages between tests. No significant correlation at submaximal exercise stages between tests 1 and 3 indicates the need for a preliminary test when the aim is to compare V˙O2 at submaximal power outputs. Without a pretest, the reason for changes in V˙O2 at the same exercise stages from one test to another could be the result of learning. No significant differences in V˙O2 at the same exercise stages and the high correlation between tests 2 and 3 mean that it is possible to compare results from one test with another. There was a 2.5% coefficient of variation in VO2 at the same exercise stage, and it was within the same magnitude as the reliability of Ergo Oxyscreen (11, 27) when measuring V˙O2(11). The linear increase in V˙O2, with increasing power output (average r = 0.997 (0.002), P< 0.001) is normal for continuous dynamical work of large muscle groups (2,16).
V˙O2peakversus V˙O2max. V˙O2peak on the ski ergometer was approximately 90% of V˙O2max when running on the treadmill and was almost the same as Mygind et al. (18) found in their study. This is higher than others have found during arm cranking or classic arm action but is reasonable considering the extensive use of trunk muscles in double poling. In addition, the subjects in these two studies are better trained, considering V˙O2max and V˙O2peak, than most other studies. In the present study with an average V˙O2peak(N = 11) of 4.55 L·min−1 (0.76), the power output was approximately 180 W. To achieve the same V˙O2 (4.90 L·min−1(0.30)) on Mygind et al's. (18) ski ergometer, the power output had to be 215 W. This could indicate use of a greater muscle mass in that study. On the other hand, the subjects could have had more upper body strength and therefore tolerated greater power output at V˙O2peak. If this was the case, the subjects would perhaps have reached V˙O2peak at 180 W if enough time was given at that exercise stage.
The present study showed no significant correlation between V˙O2max and V˙O2peak, and there were marked differences in V˙O2peak inspite of approximately the same V˙O2max. This agrees with the results of Mygind et al. (18). These are important results that do not show up during the traditional test of V˙O2max and that emphasize the importance of testing aerobic endurance in the upper body of cross-country skiers. The argument becomes even stronger considering that Mygind et al. (17) did not find a significant correlation between V˙O2max and performance but between V˙O2peak and performance. Combined with results from studies which indicate that increased muscle strength may increase aerobic endurance (8,14,26), results from the present study and the study of Mygind et al. (18) indicate that more attention should be paid to the training and testing of upper body strength and endurance of cross-country skiers.
There were no significant differences for [la−]b at V˙O2max and V˙O2peak despite significant differences in V˙O2 and power output between these two tests. [la−]b may be dependent on total work done (2,16) and the central apparati for oxygen transport, and, therefore, it would be reasonable to expect higher[la−]b at the V˙O2max-test, which incorporated the greatest muscle mass of these two tests. [la−]b is also affected by the exercising muscles ability to utilize the oxygen delivered. There is good reason to believe that, for a well-trained individual, V˙O2peak is limited by the small muscle mass involved, restricted capillary density, the mean transit time of muscle blood flow, and smaller oxidative capacity (24). A small muscle mass may lead to use of maximal force and result in high intramuscular pressures that would limit perfusion of the working muscle. A reduction in blood flow to working muscles led to an increase in anaerobic metabolism and lactate production(15,24). Considering the metabolic characteristics above, a [la−]b over 6-8 mmol·L−1 could be used as a criterion for reaching V˙O2peak on the ski ergometer as it is for reaching V˙O2max(2). No significant differences in [la−]b between the field-test and work on the ski ergometer indicate that the amount of anaerobic work in these two tests was approximately the same. On the ski ergometer fcpeak (N = 6) was 186(9.1) beats·min−1 and significantly higher than fcpeak in the field-test, which was 178 (8.6) beats·min−1. This difference may be explained by the fact that subjects worked under quite different ambient conditions in these two tests. The ambient temperature during work on the ski ergometer was 20°C while the temperature was −5°C during the field test. Another explanation may be more dynamical work with legs in the field test and, thereby, better filling of the heart and increased stroke volume compared with work on the ski ergometer.
No significant differences were found between V˙Epeak and V˙Emax on the ski ergometer and treadmill, respectively. This may have been brought about by the fact that it is not necessary to reach V˙Emax in order to reach V˙O2max(28). On the other hand, the power output on the ski ergometer could be high enough to reach V˙Emax. V˙Epeak on the ski ergometer (N = 6) was 153.7 (4.9) L·min−1 and significantly higher than V˙Epeak in the field-test, which was 133.3(6.2) L·min−1. This was not expected since no significant differences in either VO2, [la−]b, or breathing frequency were found between the tests. Finding a lower V˙Epeak in the field-test probably reflects that V˙O2peak can be reached without reaching V˙Epeak. Another explanation may be that the K2 system underestimates values for V˙E. If this was the case the values for V˙O2 also must be too low since V˙E was used for calculating V˙O2. Others (13) have found the ventilation system of the K2 to have a good reproducibility for values up to 180 L·min−1.
Conclusion. The present study showed the ski ergometer to be valid and reliable for evaluating V˙O2 in the upper body at submaximal and maximal exercise stages of cross-country skiers. No significant differences for power output (W) or V˙O2 (L·min−1), at the same exercise stages, between tests were observed. Coefficient of variation of 2.0% and 2.5% for power output and V˙O2, respectively, were observed. There were no significant differences between V˙O2peak in the field test and on the ski ergometer. The absence of significant correlation between V˙O2max and V˙O2peak highlights the need for a specific test of the upper body of cross-country skiers.
Practical applications. The ergometer used for the present study has been modified so that it is possible to change the inclination by a computer. The ski ergometer is versatile in that it allows individual arm action and is adjustable for leg actions as in classical technique in cross-country skiing. This give the opportunity for one-leg or one-arm studies for evaluating specific training effect. For evaluating strength parameters involved in the movement of the arms, both in double poling and classical technique, force parameters as peak force, time to peak force, average power and cycle length, and rate of the stride may be registered. The ergometer is also adjustable to testing or training of groups, other than cross-country skiers, where strength and endurance in the upper body are important factors. It is easy to adjust the ergometer for spesific testing of rowers, kayakers, swimmers, wheel chair users, and perhaps other groups as well.
Trying out test protocols with different inclinations will be done, as well as developing a protocol for testing anaerobic threshold in the upper body. Studies of training endurance and maximal strength in the upper body to investigate changes in aerobic endurance, heart function, and dimensions at maximal and submaximal exercise stages are already being performed.
1. Anastasia, A. Psychological Testing,
6th Ed. New York: Macmillan, 1988, pp. 115-116.
2. Åstrand, P.-O., and K. Rodahl. Textbook of Work Physiology.
New York: McGraw-Hill, 1986.
3. Bergh, U. Physiology of Cross-Country Ski Racing.
Champaign, IL: Human Kinetics, 1982.
4. Bergh, U. The influence of bodymass in cross-country skiing
. Med. Sci. Sports Exerc.
5.Clausen, J. P. Circulatory adjustments to dynamic exercise and effect of physical training in normal subjects and in patients with coronary disease. Prog. Card. Dis.
6. Dal Monte, A. Maximum oxygen consumption by telemetry. Sports Culture Rev.
7. Helgerud, J. Maximal oxygenuptake, anaerobic threshold and running performance in women and men with similar performances levels in marathons. Eur. J. Appl. Physiol.
8. Hixon, R. D., M. A. Rosenkoetter, and M. M. Brown. Strength training effects on aerobic power and short term endurance. Med. Sci. Sports Exerc.
9. Holmer, I. Physiology of swimming man. Acta Physiol. Scand. Suppl.
10. Ingjer, F. Maximal oxygen uptake as a predictor of performance ability in woman and man elite cross-country skiers. Scand. Med. Sport Exerc.
11.Instruction Manual. EOS sprint version 3.0. First ed. GmbH and CoKF, Würsburg, Germany, 1988.
12. Instruction Manual. Scan-Sense, Husøysund, Norway, 1988.
13. Kawakami, Y., D. Nozaki, A. Matsuo, and T. Fukunaga. Relability of measurement of oxygen uptake by a portable telemetric system. Eur. J. Appl. Physiol.
14. Kelly, J. M. Physiology of cross-country skiing
. In: Winter Sports Medicine, M. J. Casey, C. Foster and E. G. Hixon (Eds.). 4:227-283, 1990.
15. LeJemtel, T. H., C. S. Maskin, D. Lucido, and B. J. Chadiwicj. Failure to augment maximal limb blood flow in response to one-leg versus two-leg exercise in patients with severe heart failure. Circulation
16. McArdle, W. D., F. I. Katch, and V. L. Katch. Essentials of Exercise Physiology. Philadelphia: Lea & Febiger, 1994.
17. Millerhagen, J. O., J. M. Kelly, and T. J. Murphy. A study of combined arm and leg exercise with application to nordic skiing. Can. J. Appl. Sport Sci.
18. Mygind, E., B. Larsson, and T. Klausen. Evaluation of a specific test in cross-country skiing
.J. Sports Sci.
19. Mygind, E., L. B. Andersen, and B. Rasmussen. Blood lactate and respiratory variables in elite cross-country skiing
at racing speeds. Scand. Med. Sci. Sports
20. Ng, A. V., R. B. Demment, D. R. Basset, et al. Characteristics and performance of male citizen cross-country ski racers. Int. J. Sports Med.
21.Operator Manual. Cosmed K2 System Vacumetrics Inc. Vacumed Division, Ventura, CA, 1992.
22. Pierce, J. P., M. H. Pope, P. Renstrøm, R. J. Johnson, J. Dufek, and C. Dillman. Force measurement in cross-country skiing
.Int. J. Sports Biometr.
23.Sharkey, B. J. Training for Cross-Country Ski Racing: A Physiological Guide for Athletes and Coaches.
Champaign, IL: Human Kinetics Publishers, 1984.
24. Shephard, R. J., E. Bouhlel, H. Vanderwalle, and H. Monod. Muscle mass as a factor limiting physical work. J. Appl. Physiol.
25. Smith, G. A. Kinetic analysis of the V1 skate in cross country skiing. Proceedings of the first IOC World Congress on Sport Sciences, 1989, pp. 281-282.
26. Stone, W. J. and S. P. Coulter. Strength/endurance effects from three resistance training protocols with women. J. Strength Cond. Res.
27. Versteig, P. G. A. and Kippersluis, G. J. Automated systems for measurement of oxygen uptake during exercise testing. Int. J. Sports Med.
28. Washburn, R. A. and D. R. Seals. Comparison of continuous and discontinuous protocols for the determination of peak oxygen uptake in armcrancing.J. Appl. Physiol.
Keywords:© Williams & Wilkins 1998. All Rights Reserved.
CROSS-COUNTRY SKIING; SKI ERGOMETER; UPPER BODY; V˙O2max; V˙O2peak